1. Field of the Invention
The instant invention relates to a brake pressure boosting system for control of the brake pressure in a motor vehicle brake system equipped with an electronically adjustable brake pressure booster.
2. Discussion of the Background DE 39 43 002 A1 discloses a motor vehicle brake system, including a brake pressure booster and comprising, in addition to the usual mechanical actuating valve of the brake pressure booster, an electrically controlled valve to effect adjustment of the brake pressure booster (and thus of the braking force) in response to control signals generated by a data processor. An electronically adjustable brake pressure booster is described also in DE-GM 92 02 154.
DE 33 25 714 specifies a device for retardation of motor vehicles. Here the vehicle to be slowed down is equipped with a distance alarm radar system. With this device, the driver receives a warning when a previously set safety distance is fallen short of. If the brake pedal is actuated, following such warning, the threshold values of distance and pressure at the pedal are detected and, thereupon, an energy storage brake is activated to support the brake application in accordance with the distance and the threshold values.
DE 40 28 290 C1 describes a method of shortening the distance to stop in critical driving situations. Here, an exceeding of a first threshold value of the velocity at which the brake pedal is actuated is the only criterion to cause automatic braking at which the brake pressure acting on the brakes corresponds to the optimum brake pressure under the circumstances.
Means are known in the art with which brake pressure boosters, e.g. of a type operating with differential pressures, are controllable by an additional, electromagnetically operated control valve in such a way that a brake pressure boost is effected which differs from the purely mechanically controlled brake pressure boosting, being effected in response to the electronic control commands for the electromagnetically operable control valve.
Behavioral studies of drivers driving vehicles that are equiped with ABS (antilock braking system) have demonstrated that erroneous reactions often occur unconsciously in critical driving situations (especially so-called panicky braking). It is true, the brake pedal very often is actuated quickly enough during the initial phase of a braking operation, yet many drivers hesitate to slam down the pedal with maximum force. With a great number of car drivers, this braking performance, which certainly is not the optimum, occurs for the following reasons:
During the initial phase of a braking operation, the hydraulic reactive force (counter-force) acting against the pressure of the brake pedal still is relatively small because it is being generated by the rising pressure in the brake system. Therefore, the driver readily increases the velocity of actuation at the beginning of a brake application process. However, the reactive force augments very fast in the course of the further pedal travel. For this reason it can be observed with a great many drivers that, on panicky braking, the pedal velocity drops again rather quickly after having reached the maximum. Therefore, normally, distance to come to a stop is given away with this course of pedal actuation.